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583B.cpp
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583B.cpp
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/**
* Author : Rohit Kumar Kerketta
* Coder!
* #NeverGiveUp!
**/
#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
typedef long double ldb;
typedef long long int ll;
#define pb push_back
#define For1(i,a,n) for (i = (a); i<(n); i++)
#define For2(j,a,n) for (j = (a); j<(n); j++)
#define For3(k,a,n) for (k = (a); k<(n); k++)
#define For1e1(i,a,n) for (i = (a); i<=(n); i++)
#define For2e2(j,a,n) for (j = (a); j<=(n); j++)
#define For3e3(k,a,n) for (k = (a); k<=(n); k++)
#define For1r(i,a,n) for (i = (a); i>(n); i--)
#define For2r(j,a,n) for (j = (a); j>(n); j--)
#define For3r(k,a,n) for (k = (a); k>(n); k--)
#define For1e1r(i,a,n) for (i = (a); i>=(n); i--)
#define For2e2r(j,a,n) for (j = (a); j>=(n); j--)
#define For3e3r(k,a,n) for (k = (a); k>=(n); k--)
#define SortA(n,x) sort(n,n+x);
#define SortV(s) sort(s.begin(), s.end());
#define SortVR(s) sort(s.rbegin(), s.rend());
#define Search(s) s.begin(), s.end()
#define SortDec(n) sort(n.begin(), n.end(), greater<int>());
#define inp(a) cin>>a;
#define inStr(a) getline(cin,a);
#define Size(a) a.size()
#define inp2(a,b) cin>>a>>b;
#define inp3(a,b,c) cin>>a>>b>>c;
#define inp4(a,b,c,d) cin>>a>>b>>c>>d;
#define Unique(n) sort(Search(n)),n.erase(unique(Search(n)),n.end())
#define PI 3.1415926535897932384626433832795l
#define Ignore cin.ignore();
#define pf(n) cout<<n
#define nl endl;
#define sp " ";
#define mem(n,i) memset(n,i,sizeof n);
#define deci(n) cout<<fixed<<setprecision(n);
#define square(n) n*n
#define cube(n) n*n*n
#define F first
#define S second
#define bug() cout<<"*****<>*****\n";
#define s1(n) scanf("%d",&n)
#define s2(n,k) scanf("%d %d",&n,&k)
#define s3(a,b,c) scanf("%d %d %d",&a,&b,&c)
#define s4(n,k,a,b) scanf("%d %d %d %d",&n,&k,&a,&b)
#define mp(x,y) make_pair(x,y);
#define F first
#define S second
typedef stringstream SS;
typedef vector<string> VS;
typedef vector<ll> VLL;
typedef vector<ull> VULL;
typedef vector<int> VI;
typedef vector<char> VC;
typedef map<string, string> MSS;
typedef map <ll,string> MLLS;
typedef map <char,ll> MCLL;
typedef map <string,ll> MSLL;
typedef map <ll,ll> MLLLL;
typedef pair<int, int> pii;
template <typename T> inline T ItoS(T n){SS a; a<<n;return a.str();}
template <typename T> inline T TrailingZeros(T n){ll cnt = 0;for(ll i=5; n/i>=1; i*=5) cnt += n/i;return cnt;}
template <typename T> inline T StoI(T s){ll sum=0;for(ll i=0; i<Sz(s); i++){s[i]-='0';sum=sum*10+s[i];}return sum;}
template <typename T> inline T binary_decimal(T n){ll decimal=0, i=0, rem;while (n!=0){rem = n%10;n/=10;decimal += rem*pow(2,i);++i;}return decimal;}
template <typename T> inline T LCM(T a,T b){return (a*b)/GCD(a,b);}
template <typename T> inline T maxi(T x, T y) { if(x>y) return x; else return y;}
template <typename T> inline T maxi(T x, T y,T z) { return maxi(maxi(x,y),z);}
template <typename T> inline T mini(T x, T y) { if(x<y) return x; else return y;}
template <typename T> inline T mini(T x, T y,T z) { return mini(mini(x,y),z);}
template <typename T> inline T GCD(T a,T b) {ll t;while(a){t = a;a = b%a;b = t;}return b;}
template <typename T> inline T Pow(T base,T exp){ll result = 1;while (exp){if(exp&1)result*=base;exp>>=1;base*=base;}return result;}
template <typename T> inline T Mulmod(T a, T b, T c){ull x = 0,y = a%c;while(b>0){if(b&1) x = (x+y)%c;y = (y<<1)%c;b >>= 1;}return x;}
template <typename T> inline T Pow(T base,T exp,T mod){ull x = 1, y = base;while(exp>0){if(exp&1) x = Mulmod(x,y,mod);y = Mulmod(y,y,mod);exp >>= 1;}return x;}
template <typename T> inline T modulo(T a,T b,T c){ull x = 1 , y = a%c ;while( b>0 ){if(b%2) x = Mulmod(x,y,c) ;y=Mulmod(y,y,c);b/=2;}return x%c ;}
template <typename T> inline T BigMod(T a, T b, T m){if(!b)return 1;ll x=BigMod(a, b/2, m);x=(x*x)%m;if(b%2)x=(x*a)%m;return x;}
template <typename T> inline T EGCD(T a,T b,T &x,T &y){if(a == 0) {x = 0;y = 1;return b;}T x1, y1;T d = EGCD(b % a, a, x1, y1);x = y1 - (b / a) * x1;y = x1;return d;}
/****************** Prime Generator **********************/
const int N=1e7+7; int prime[20000010]; bool isprime[N]; int nprime;
ull mod = 1000000007;
template <typename T> void Sieve(T a){nprime = 0;memset(isprime,true,sizeof(isprime));isprime[1]=false;for(int i=2;i<N;i++){if(isprime[i]){prime[nprime++]=i;for(int j=2;i*j<N;j++)isprime[i*j]=false;}}}
template <typename T> bool miller_rabin(T p, T itt) {if(p<2) return 0 ;if(p==2) return 1;if(p%2==0) return 0 ;ull s = p-1 ;while(s%2==0) s/=2;for(ll i=1;i<=itt;i++) {ull a = rand() % (p-1)+1 , temp = s ;ull mod = modulo(a,temp,(ull)p);while(mod!=1 and mod!=p-1 and temp!=p-1){mod = Mulmod(mod,mod,(ull)p);temp*=2;}if(temp%2==0 and mod!=p-1) return false ;}return true;}
template <typename T> inline T PrimeFactors(T n){ll cnt=0,sum=1;for(int i=0; prime[i]*prime[i]<=n and i<nprime;i++){cnt=0;while(n%prime[i]==0){cnt++;n/=prime[i];}sum*=(cnt+1);}if(n>1)sum*=2;return sum;}
/****************** Geometry *****************/
template <typename T> inline T PointDistanceHorVer(T x1,T y1,T x2, T y2) {return abs(x1-x2)+abs(y1-y2);}
template <typename T> inline T PointDistanceDiagonally(T x1,T y1,T x2, T y2) {return sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));}
template <typename T> inline T PointDistanceMinimum(T x1,T y1,T x2, T y2) { T tmp1=abs(x1-x2); T tmp2=abs(y1-y2); T tmp3=abs(tmp1-tmp2); T tmp4=min(tmp1, tmp2); return tmp3+tmp4; }
template <typename T> inline T PointDistance3D(T x1,T y1,T z1,T x2,T y2,T z2) {return sqrt(square(x2-x1)+square(y2-y1)+square(z2-z1));}
template <typename T> inline T Cube(T a){return a*a*a;}
template <typename T> inline T RectengularPrism(T a,T b,T c){return a*b*c;}
template <typename T> inline T Pyramid(T base, T height){return (1/3)*base*height;}
template <typename T> inline T Ellipsoid(T r1,T r2,T r3) {return (4/3)*PI*r1*r2*r3;}
template <typename T> inline T IrregualarPrism(T base, T height){return base*height;}
template <typename T> inline T Sphere(T radius){ return (4/3)*PI*radius*radius*radius;}
template <typename T> inline T CylinderB(T base, T height){return base*height;} // base and height
template <typename T> inline T CylinderR(T radius, T height){return PI*radius*radius*height;} // radius and height
template <typename T> inline T Cone (T radius,T base, T height){return (1/3)*PI*radius*radius*height;}
template <typename T> inline void pfArr(T vec){ int i; For1(i,0,vec.size()) cout<<vec[i]<<" "; }
ll max(ll m,ll n){ return (m>n)?m:n;}
ll min(ll m,ll n){ return (m<n)?m:n;}
/**>>>>>>>>>>>>>>>>>>> END <<<<<<<<<<<<<<<<<<**/
int main(){
int n,i;
s1(n);
VLL arr(n);
For1(i,0,n)
cin>>arr[i];
ll cnt = 0;
ll res = 0;
VLL all(n,0LL);
ll allcnt = 0;
bool f = 0;
bool r = 0;
while(true){
For1(i,0,n){
if(!f){
f = 1;
cnt++;
}
if(arr[i]<=res && !all[i]){
res += 1;
all[i] = 1;
allcnt++;
}
if(allcnt==n)
break;
}
if(allcnt==n)
break;
For1e1r(i,n-1,0){
if(!r){
r = 1;
cnt++;
}
if(arr[i]<=res && !all[i]){
res += 1;
all[i] = 1;
allcnt++;
}
if(allcnt==n)
break;
}
f = 0;
r = 0;
if(allcnt==n)
break;
}
cout<<cnt-1;
return 0;
}